Volatile oil
Volatile oils
• different from fixed
– secreted in oil cells in specialised structures
• ducts, gland, cell or glandular hairs
– frequently associated with other substances
• gums, resins (resinify on exposure to air)
• mainly terpenoid
– some phenol ethers and phenols
• Terpenoids
– based on the 5C isoprene unit
– Monoterpenes
• most important, most volatile
– di-, tri-, sesquiterpenes also important
• contain 2 condensed 5C units head-tail
Monoterpene components
• Hydrocarbons
• Alcohols
• Aldehydes
Citral
– all produced via the terpenoid pathway
• Ketones
• Esters
• Oxides
Sesquiterpenes (C15)
Hydrocarbons
Phenols
Phenolic
esters
Anethole
Chemical and physical properties
• volatile liquids with no colour
– keep in amber bottles with minimum air
• odour
• asymetric centres, isomers with optical activity
– only one isomer occurs naturally
• refractive index normally high
– is a means to characterise the oil
• miscible in water and soluble in organic solvents
– more soluble if contains –OH fatty acids
• reasonably heat stable
– can be steam distilled
• tend to be used as solvents for resins
Families
• Economically only a few family groups are
commercially useful
[1] Labiatae
Lavender, Mentha Sp.
• oil occurs in special organs
– synthesized in glandular trichomes (mint)
[2] Umbelliferae
Fruits (best if ripe): anise, caraway, fennel, coriander
• found in “vittae” in the outer layer is characteristic
[3] Pinaceae
Pine, juniper
• found in resin ducts in outer old xylem or bark
• released when bark removed
[4] Rutaceae
Citrus fruits
• typical ductless sacs in outer part of fruit – rind
• less stable, need more care
[5] Lauraceae
Cinnamon, camphor
• from region immediately below bark
Uses
as inhalations, orally, gargles, mouthwashes, trans-dermally
[1] Flavours & carminatives
[2] Local stimulants and antiseptics
(containing phenols)
[3] Perfumes
[4] Insect repellant, antimating device
[5] Starting materials